Glycemic Index Approach to Your Diet – Pros and Cons

low gi / gl

Earlier this summer, research published in the Journal of the American Medical Association added a new twist to the classic low fat vs. low carb diet debate. Measurements of bodily energy expenditure and hormone levels were taken of 3 groups of people who had partaken in recent weight loss and were now in weight maintenance mode. The three groups ate one of 3 diet types:

  1. low-fat diet (60% of energy from carbohydrate, 20% from fat, 20% from protein; high glycemic load)
  2. low–glycemic index diet (40% from carbohydrate, 40% from fat, and 20% from protein; moderate glycemic load)
  3. very low-carbohydrate diet (10% from carbohydrate, 60% from fat, and 30% from protein; low glycemic load)

The group with the best outcome after several weeks?

Group number 2, consuming a low glycemic diet, fared the best. The low fat diet slowed down the metabolism the most. The low carb diet negatively affected hormone levels, increasing chances of inflammation and disease.

Conclusion: a low glycemic index diet as the best approach to weight loss and maintenance over time.

But what exactly is a low glycemic index diet? What is glycemic load?  What you need to know:

The glycemic index (GI) is a measurement of how a food raises blood glucose levels. Blood glucose is colloquially referred to as blood sugar.GI is an important measurement for people living with diabetes who need to control their blood glucose through diet, oral medication, and insulin injections. But it is also important for healthy individuals because spikes in blood sugar often come with a crash an hour or 2 later which leads to hunger pangs and a tendency to eat more. This leads to a vicious cycle of overeating and weight gain, and eventually can lead to diabetes.

The glycemic index range is 0-100. The higher the GI, the more blood glucose will rise. Pure glucose has a GI of 100.

  • High GI – 70 and up
  • Medium GI – 55-69
  • Low GI – 55 or lower

Refined carbohydrates have a high glycemic index, but unprocessed carbs from fresh produce and whole grains usually have a low to medium GI. Meats usually have a low glycemic index.

The system sounds great in theory. It would be wonderful if every food item had a little label telling us its glycemic index. Unfortunately, there are several practical limitations:

  1. The glycemic index is not something than can be calculated or imputed simply by examining a food’s nutrient make or its ingredients. The data is collected by measurement of a food’s effect on real people’s blood glucose under very controlled conditions in a lab. To date, only a few thousand foods have been measured this way. measurements for the same food item can vary by tens of percentage points. An apple for example has been recorded with values of 28, 32, 34, and 44.
  2. Additionally, the glycemic index. found in various data tables, discusses the effect of a single food product in isolation. Lets assume an apple’s glycemic index is  34. If you are eating it with some nuts, the GI will be totally different. A baked potato has a very high GI, but eaten with a small piece of chicken, will actually have a medium GI.
  3. Lastly, the glycemic index does not take into account a food’s serving size. This is where the Glycemic Load (GL), comes into play.

Glycemic Load is a better indicator for the rise in blood glucose because it takes into account the actual portion size consumed. Glycemic load is defined as the grams of available carbs in a serving times its GI divided by 100.

  • High GL – 20 or higher
  • Medium GL – 11-19
  • Low GL – 10 or lower

An apple with a glycemic index of 34 will have a glycemic load of only 7 for a 3 ounce serving. A double sized serving will double the glycemic load.

Additional factors that affect the glycemic index of foods:

  • Ripeness and storage time – the more ripe a fruit or vegetable is, the higher the GI
  • Processing – juice has a higher GI than whole fruit; mashed potato has a higher GI than a whole baked potato, stone ground whole wheat bread has a lower GI than whole wheat bread.
  • Cooking method: how long a food is cooked (al dente pasta has a lower GI than soft-cooked pasta)
  • Variety: converted long-grain white rice has a lower GI than brown rice but short-grain white rice has a higher GI than brown rice.

Important! Many nutritious foods have a higher GI than foods with little nutritional value. For example, oatmeal has a higher GI than chocolate. Use of the glycemic index needs to be balanced with basic nutrition principles of variety for healthful foods and moderation of foods with few nutrients.

What to do at the supermarket:

You won’t find the GI / GL of products on the packaging, albeit a few rare cases. However, if you choose whole grains, fresh or frozen produce, lean meats and dairy, and add legumes, nuts, and healthy oils, you are on the right track. Don’t forget that  calories from a diet of real foods are still calories. Eat too many, and you will gain weight.

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  • Carol

    “It would be wonderful if every food item had a little label telling us its glycemic index.” Actually, it is naive to think such innately imprecise (and irrelevant) info would have any more benefit than simply following age-old common-sense dietary rules that for some reason still get no respect. Having a number attached to a food (especially when it means nothing in the real world, where we eat more than one ingredient at a time) is still not going to prevent overeating. We are not lab subjects in a controlled-calorie experiment… we are humans going about our lives with many food choices. The sooner this GI stuff (and other “magic” formulas/diets) goes away the sooner people might start paying attention to simply eating better foods (I think they know more or less what those are) and monitoring how much they eat (e.g., looking at serving sizes on packages to understand that the nutrition data is for a finite amount of food). What are people not getting about balance, variety and moderation that they continue to be conned by simplistic dietary “solutions”?

  • Michele Hays

    Right. One of the many things that ticks me off about Nutella’s marketing campaign is that they’ve gotten themselves listed as a low glycemic food. Apparently ingesting huge amounts of fat with refined sugar changes its glycemic load.

    I think, like any other diet system, this one works only as long as you don’t cheat, even when highly-processed products encourage you to.

  • Judy Wyatt

    “mashed potato has a higher GI than a whole baked potato”

    Why would mashing a potato in a bowl prior to eating it result in a higher GI than mashing a baked potato by chewing it?

    • Carol

      The GI value for mashed is probably for skinless (most of the fiber is in the skin), so if you leave the skin on it should be the same.

      • Judy Wyatt

        Thank you, Carol. That makes sense. I eat the skins regardless of how I prepare potatoes.

        And of course it makes sense that portion sizes and other foods in the meal (Points 2 & 3 in the article above) make a difference in how the body responds to specific foods. Plus, something that the demonizers of certain foods (potatoes! I’m gonna die!!!) and the sanctifiers of certain foods (blueberries and broccolli! I’ll live forever!!!) leave out of the equation is that we are all different. There is no one diet that is appropriate for everyone.

        I’ll give the glycemic index a pass, thanks.

        • Kitteh

          There is no one diet that is appropriate for everyone. – Captain Obvious to the rescue!!! Thanks for your input, it is very valuable and translates roughly as “there is no point in nutritional science, we’re all different anyway”.

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